JP7574102B2 - Duplex printing device - Google Patents

Description

The present invention relates to a double-sided printing device that performs double-sided printing on print media.

Conventionally, there is known a double-sided printing device that circulates print media that has been printed on one side, switches it back at a reversing section to invert it, and then prints on the other side. In recent years, there has been an increasing demand for printing devices to improve productivity through high-speed printing, and there is a demand for high productivity through high-speed printing not only when printing on one side, but also when printing on both sides.

When printing on one side, printing paper can be fed one after the other, so the printing unit performing the printing process can output the number of prints per unit time that the printing medium can produce. On the other hand, when printing on both sides, the printing medium that has been printed on the front side is circulated and transported, then turned over and the back side is printed, so the double-sided transport speed during circulating transport affects the productivity of the printing device. In other words, if the double-sided transport speed is not appropriate, a situation may arise in which the printing medium is not transported to the printing unit even though printing processing by the printing unit is possible, and the same productivity as when printing on one side cannot be ensured.

Double-sided printing requires two printing processes for single-sided printing. Therefore, if the number of sheets output per unit time during double-sided printing is half the number of sheets output during single-sided printing, double-sided printing can be performed with the same productivity per side as single-sided printing.

In order to ensure the same productivity during double-sided printing as during single-sided printing, Patent Document 1 proposes a method of calculating the number of circulating sheets of printing medium based on the size of the printing medium, the paper spacing (sheet interval), and the printing speed, and determining a double-sided transport speed that can ensure the above-mentioned productivity based on the number of circulating sheets. Note that in this specification, the printing speed refers to the transport speed of the printing medium when printing is being performed by ejecting ink onto the printing medium, etc.

Patent Document 1 also proposes that, in order to avoid collisions of print media within the circulatory transport path, if the double-sided transport speed is lower than the printing speed, the number of circulating sheets is reduced and the double-sided transport speed is recalculated. Note that if the double-sided transport speed is lower than the printing speed, the double-sided transport speed of the print media being circulated is slower than the transport speed of the print media being discharged from the printing unit, so the leading edge of the subsequent print medium discharged from the printing unit will collide with the print medium being circulated and transported first.

However, when the number of circulating sheets is reduced to increase the double-sided transport speed as described above, the double-sided transport speed may exceed the rated rotation speed of the motor of the transport mechanism. Therefore, Patent Document 1 proposes that in this case, the paper spacing (paper gap) of the print media is widened to calculate a double-sided transport speed that does not exceed the rated rotation speed of the motor.

JP 2009-46303 A

However, if the double-sided conveying speed is reduced by adjusting the paper spacing, as in the method of Patent Document 1, there is a problem that the productivity of double-sided printing decreases.

In view of the above circumstances, the present invention aims to provide a duplex printing device that can calculate a duplex conveying speed that does not cause conveying problems and maintains productivity.

The double-sided printing device of the present invention includes a printing unit that performs printing processing on the printing medium, a registration unit that feeds the printing medium toward the printing unit at regular intervals, a reversing unit that receives the printed printing medium that has been printed on one side by the printing unit and reverses and discharges the printed printing medium, and a control unit that controls the conveying speed of the printing medium. The control unit calculates the number of sheets of printing medium in the conveying path of the printing medium and the double-sided conveying speed when the printed printing medium is circulated and refed to the registration unit based on the size and printing speed of the printing medium, and if the calculated double-sided conveying speed is outside a preset range, the control unit changes the number of sheets of printing medium in the conveying path and the control conditions of the reversing unit to recalculate the double-sided conveying speed.

According to the duplex printing device of the present invention, the number of sheets of printing media in the transport path of the printing media and the duplex transport speed when circulating and re-feeding the printed printing media to the registration section are calculated based on the size and printing speed of the printing media. If the calculated duplex transport speed is outside a preset range, the number of sheets of printing media in the transport path and the control conditions of the inversion section are changed and the duplex transport speed is recalculated, so that a duplex transport speed that does not cause transport problems and maintains productivity can be calculated. The effect of changing the number of sheets of printing media in the transport path and the control conditions of the inversion section on the duplex transport speed will be described in detail later.

FIG. 1 is a diagram showing a schematic configuration of a first embodiment of an inkjet printing apparatus according to the present invention; FIG. 2 is a block diagram showing a schematic configuration of a control system of the inkjet printing apparatus shown in FIG. FIG. 2 is a timing chart for explaining the print medium transport operation of the inkjet printing device shown in FIG. Diagram for explaining the print schedule when printing on both sides FIG. 1 is a diagram for explaining a collision of print media when the double-sided transport speed is slower than the printing speed; A flowchart for explaining a method for adjusting the double-sided transport speed in the inkjet printing apparatus shown in FIG. A flowchart for explaining a method for adjusting a duplex conveying speed in consideration of a paper gap according to a time required for post-processing FIG. 2 is a diagram showing a schematic configuration of a second embodiment of an inkjet printing apparatus according to the present invention; FIG. 9 is a block diagram showing a schematic configuration of a control system of the inkjet printing apparatus shown in FIG. A timing chart for explaining the print medium transport operation of the inkjet printing device shown in FIG. A flowchart for explaining a method for adjusting the double-sided transport speed in the inkjet printing apparatus shown in FIG.

A first embodiment of an inkjet printing device of the present invention will be described in detail below with reference to the drawings. The inkjet printing device of this embodiment is characterized by control of the transport speed of the print medium during double-sided printing, but first, its overall configuration will be described. Figure 1 is a diagram showing the schematic configuration of an inkjet printing device 1 of this embodiment. Note that the up, down, left, and right directions shown in Figure 1 are the up, down, left, and right directions of the inkjet printing device 1 of this embodiment. Also, the front side of the paper in Figure 1 is the front direction, and the back side of the paper is the rear direction.

As shown in FIG. 1, the inkjet printing device 1 of this embodiment includes a side paper feed section 10, an internal paper feed section 20, a printing section 30, a paper discharge section 40, and an inversion section 50.

The printing unit 30 and the internal paper feed unit 20 are housed and installed in a housing made of metal or resin. The side paper feed unit 10 and the paper discharge unit 40 are installed with a part of them housed within the housing and a part protruding outside the housing.

The side paper feed unit 10 includes a paper feed tray 11 on which the print medium P is placed, a primary paper feed unit 12 that feeds and transports only the topmost print medium P from the paper feed tray 11, and a secondary paper feed unit 14 that sends the print medium P transported by the primary paper feed unit 12 to the printing unit 30 at a predetermined timing.

The primary paper feed unit 12 includes a paper feed roller and a paper feed motor that drives the paper feed roller.

The secondary paper feed unit 14 includes a registration roller 14a that is brought into contact with the leading edge of the print medium P transported from the primary paper feed unit 12 or the print medium P transported from the internal paper feed unit 20, which stops the print medium P temporarily to form slack, thereby correcting skew, and a registration motor that drives the registration roller 14a. In this embodiment, the secondary paper feed unit 14 corresponds to the registration unit of the present invention.

The internal paper feed unit 20 includes a paper feed tray 21a on which the print medium P is placed, a primary paper feed unit 22a that feeds and transports only the topmost print medium P from the paper feed tray 21a, a paper feed tray 21b on which the print medium P is placed, a primary paper feed unit 22b that feeds and transports only the topmost print medium P from the paper feed tray 21b, transport rollers 23, and vertical transport rollers 15.

The primary paper feed units 22a and 22b are equipped with paper feed rollers and a paper feed motor that drives the paper feed rollers.

The print medium P fed from the paper feed tray 21a by the primary paper feed unit 22a and the print medium P fed from the paper feed tray 21b by the primary paper feed unit 22b are transported by the transport rollers 23 toward the vertical transport rollers 15.

The vertical conveying rollers 15 are provided on the conveying path between the registration rollers 14a and the conveying rollers 23, and between the registration rollers 14a and the second double-sided conveying rollers 45 described later.

Therefore, the vertical transport rollers 15 transport the print medium P from the primary paper feed units 22a and 22b, and also transport the print medium P from the inversion unit 50 described below. Therefore, just before the vertical transport rollers 15 in the transport direction, there is a junction where the transport path of the print medium P fed from the internal paper feed unit 20 and the transport path of the print medium P with one side printed and transported from the inversion unit 50 join together.

In this embodiment, the transport path from the registration roller 14a to the reversing roller 52 described later via the printing unit 30 and the first duplex transport roller 44 described later is called the first duplex transport path DS1, with the registration roller 14a as the reference point. The transport path from the reversing roller 52 to the registration roller 14a via the second duplex transport roller 45 and the vertical transport roller 15 described later is called the second duplex transport path DS2. The transport path from the second belt platen roller 34 described later to the paper discharge unit 40 is called the paper discharge transport path HS, and the transport path where the print medium P switches back at the reversing unit 50 is called the reverse transport path SR.

Furthermore, a number of paper detection sensors that detect the print medium P are provided on the transport paths of the print medium P, such as the first double-sided transport path DS1, the second double-sided transport path DS2, the discharge transport path HS, and the reverse transport path SR, and the transport of the print medium P is controlled by the control unit 60, which will be described later, based on the detection signals detected by the paper detection sensors. In particular, a reverse transport sensor RS is provided on the first double-sided transport path DS1 between the most downstream first double-sided transport roller 44 and the reverse roller 52, near the downstream side of the first double-sided transport roller 44. The reverse transport sensor RS is also a sensor that detects the print medium P.

The printing unit 30 includes four line heads 31, a circular conveyor belt 32 arranged opposite the line heads 31, a first belt platen roller 33, and a second belt platen roller 34.

The conveyor belt 32 is formed of a circular endless belt and has many suction holes formed therein. The print medium P fed from the secondary paper feed unit 14 is conveyed to the circular conveyor belt 32. The print medium P is then adsorbed onto the conveyor belt 32 by the suction of a suction fan (not shown) installed on the back side of the conveyor path surface of the conveyor belt 32, and is conveyed at a predetermined conveying speed. Then, while the print medium P is conveyed by the conveyor belt 32, ink is ejected from the line head 31 onto the print medium P, thereby performing a printing process on the print medium P.

The conveyor belt 32 is stretched across the first belt platen roller 33 and the second belt platen roller 34, and the first belt platen roller 33 and the second belt platen roller 34 are driven by a conveyor motor (not shown), causing the conveyor belt 32 to rotate clockwise in FIG. 1.

Each line head 31 extends in a direction perpendicular to the transport direction of the print medium P, and ejects ink onto the print medium P transported by the transport belt 32. As shown in FIG. 1, the four line heads 31 are arranged at predetermined intervals along the transport path of the print medium P. Each of the four line heads 31 ejects CMYK ink.

Each line head 31 has a head row in which three inkjet heads are arranged at equal intervals in a direction (front-to-back direction) perpendicular to the transport direction of the print medium P. Each line head 31 has two head rows, which are arranged in a staggered pattern so that the inkjet heads in each head row overlap by a predetermined number of nozzles.

Then, one line of printed image is formed by printing using the inkjet heads in the two head rows that each line head 31 has.

A switching mechanism 43 is provided at the junction of the first double-sided transport path DS1 and the discharge transport path HS. The switching mechanism 43 switches between guiding the print medium P that has been printed in the printing unit 30 to the discharge unit 40 or circulating it on the first double-sided transport path DS1.

The paper discharge section 40 has a tray-shaped paper discharge stand 41 that protrudes from the housing of the inkjet printing device 1, and three pairs of paper discharge rollers 42 that discharge the print medium P onto the paper discharge stand 41. The print medium P that is guided to the paper discharge transport path HS by the switching mechanism 43 is discharged onto the paper discharge stand 41 by the paper discharge rollers 42.

The reversing unit 50 includes a reversing transport path SR that reverses the print medium P, a reversing roller 52 that transports the print medium P from the first double-sided transport path DS1 to the reversing transport path SR and switches back the print medium P transported to the reversing transport path SR to return it to the second double-sided transport path DS2, and a reversing motor (not shown) that drives the reversing roller 52.

The print medium P guided to the first double-sided transport path DS1 by the switching mechanism 43 is transported from the first double-sided transport path DS1 to the reverse transport path SR by the first double-sided transport rollers 44. The print medium P is then returned from the reverse transport path SR to the second double-sided transport path DS2 by the reverse rollers 52, so that the print medium P is transported on the second double-sided transport path DS2 in an inverted state. The inverted print medium P is then transported towards the vertical transport rollers 15 by the second double-sided transport rollers 45 provided on the second double-sided transport path DS2.

The print medium P transported by the vertical transport rollers 15 is transported again to the registration rollers 14a of the secondary paper feed section 14, and is sent out again toward the printing section 30 at a predetermined timing by the registration rollers 14a. Then, the printing section 30 applies printing processing to the back side of the print medium P.

The print medium P, whose back side has been printed by the printing unit 30, is guided to the discharge transport path HS by the switching mechanism 43 and discharged onto the discharge tray 41 by the discharge rollers 42.

Figure 2 is a block diagram showing the schematic configuration of the control system of the inkjet printing device 1 of this embodiment. As shown in Figure 2, the inkjet printing device 1 includes a control unit 60 and an operation panel 70.

The control unit 60 controls the entire inkjet printing device 1 and includes a CPU (Central Processing Unit) and a semiconductor memory. The control unit 60 controls the operation of each part of the inkjet printing device 1 by having the CPU execute a program that is pre-stored in the semiconductor memory.

The control unit 60 also acquires image data output from a computer or image data read by a scanner, and performs printing processing by controlling the printing unit 30 based on the image data.

The control unit 60 also acquires printing conditions such as the size and printing speed of the print medium P, and performs processes such as calculating the double-sided transport speed of the print medium P, which will be described later, and calculating the number of sheets of paper along the transport path of the print medium P, based on the printing conditions.

The operation panel 70 is composed of a touch panel with a liquid crystal display, and displays various setting input screens and accepts various setting inputs such as input of instructions to start printing and input of settings for printing conditions. The size of the print medium P obtained by the control unit 60 is set and input, for example, on the operation panel 70. In addition, the size of the print medium P may be detected by a sensor installed on the paper feed tray of the side paper feed unit 10 and the internal paper feed unit 20.

Next, the transport operation of the print medium P of the inkjet printing device 1 of this embodiment will be described with reference to the timing chart shown in FIG. 3. Note that the horizontal axis of FIG. 3 represents time, and the vertical axis represents the transport speed of the print medium P. Also, the transport operation during double-sided printing will be described here.

First, the leading edge of the print medium P transported by the side feeder 10 or the internal feeder 20 comes into contact with the registration roller 14a, and the medium stops once a slack is formed.

Then, at time t1, the print medium P is transported by the registration rollers 14a toward the printing unit 30. At this time, the secondary paper feed unit 14 accelerates at an acceleration α1, and then transports the print medium P at a transport speed _V1 .

Then, the secondary paper feed unit 14 subsequently decelerates at a deceleration rate α2, and at time t2 when the conveying speed reaches _V2, delivers the print medium P to the conveying belt 32. Note that the relationship between the conveying speed _V1 and the conveying speed _V2 is _V1 > _V2 , as shown in FIG. 3. This allows the gap between the sheets to be narrowed.

The conveyor belt 32 is also driven at a conveying speed _V2 , and conveys the print medium P received from the secondary paper feed unit 14 at a constant speed of conveying speed _V2 . Then, the printing unit 30 performs a printing process on the front side of the print medium P conveyed at the conveying speed _V2 . The print medium P sent out from the conveyor belt 32 is then continuously conveyed at the constant speed of conveying speed _V2 by the first double-sided conveying roller 44 and the reversing roller 52.

Then, when the rear end of the print medium P reaches the reverse transport sensor RS (time t3), the reverse rollers 52 accelerate at an acceleration α3 and transport the print medium P at a constant transport speed _V3 . The print medium P is guided to the reverse transport path SR by the transport by the reverse rollers 52.

After the print medium P is guided to the reverse transport path SR, the reverse roller 52 decelerates at a deceleration rate α4 to stop the print medium P by switching back. Then, when the rear end of the print medium P reaches a position that is a distance Ls (amount of rear end remaining when reversing) away from the reverse roller 52, the reverse roller 52 stops (time t4).

The trailing end remaining amount Ls during reversal is set in advance as a distance by which the printing medium P can be sufficiently drawn into the reversing transport path SR so that it can be reversed, and the printing medium P can be transported in both directions without coming off the reversing rollers 52. Therefore, the deceleration start position of the reversing rollers 52 is a position at which the trailing end of the printing medium P can stop at a position the distance Ls from the reversing rollers 52 when it is decelerated from the transport speed _V3 at the deceleration rate α4.

Then, at time t5, which is the reversing section wait time from time t4 when the reversing rollers 52 temporarily stopped transporting the print medium P, the reversing rollers 52 resume rotating in the reverse direction, and the print medium P is switched back and transported. The reversing section wait time SB _wait from time t4 to time t5 is initially set to an initial value, but is changed as necessary when calculating the double-sided transport speed, which will be described later.

Then, after the print medium P starts to be reversed, the print medium P is accelerated and transported at an acceleration α3 by the reversing roller 52 and the second double-sided transport roller 45. When the print medium P reaches a transport speed _V4 , it is transported at a constant speed by the second double-sided transport roller 45 and the vertical transport roller 15.

Thereafter, in order to stop the printing medium P at the registration rollers 14a, the second double-sided conveying rollers 45 and the vertical conveying rollers 15 decelerate at a deceleration rate α5. In this embodiment, the printing medium P is conveyed at a constant speed at a conveying speed _V5 while being decelerated at the deceleration rate α5. In this way, by conveying the printing medium P at a constant speed once before the leading edge of the printing medium P abuts against the registration rollers 14a of the secondary paper feed unit 14, the speed at which the printing medium P collides with the registration rollers 14a can be slowed down, and the collision sound can be reduced. However, it is not necessary to provide this constant speed conveying period.

Furthermore, the deceleration start position of the second double-sided transport roller 45 and the vertical transport roller 15 described above may be a position where the leading edge of the print medium P can stop in the secondary paper feed unit 14 when the print medium P is decelerated from the transport speed _V4 at the deceleration rate α5. However, in the secondary paper feed unit 14, the print medium P comes into contact with the secondary paper feed unit 14 once and is corrected for skew as described above, so the print medium P stops with slack. The amount of slack formed during the skew correction is set in advance.

Then, at time t7, which is a preset registration start waiting time from time t6 when the second double-sided conveying roller 45 and the vertical conveying roller 15 stop conveying the print medium P, the registration roller 14a starts rotating and the print medium P is sent out toward the printing unit 30.

Then, the operation from time t1 shown in FIG. 3 is repeated, and the back side is printed by the line head 31 while the transport belt 32 transports the sheet at a constant transport speed _V2 .

The print medium P with the back side printed is guided by the switching mechanism 43 to the discharge transport path HS on the discharge tray 41 side, and is discharged by the discharge rollers 42 at a transport speed suitable for discharge.

Next, we will explain the printing schedule for double-sided printing.

The inkjet printing device 1 of this embodiment is capable of feeding a subsequent printing medium P before the preceding printing medium P is discharged. Therefore, for example, after printing the front side of a first sheet of printing medium P, a second sheet of printing medium P can be fed and the front side of the second sheet printed before the first sheet of printing medium P is turned over in the circulating transport and printed on its back side. Therefore, when multiple sheets of printing media can be circulated, it is necessary to schedule the order in which to print each side of the printing medium P in double-sided printing.

When multiple sheets of print media P can be circulated, the printing order is such that the front side of a newly fed print medium P and the back side of a print medium P that has been circulated along the first double-sided transport path DS1 and the second double-sided transport path DS2 are printed alternately, thereby increasing productivity.

For example, when two sheets of print media P are circulated, as shown in FIG. 4(a), the front side of the first sheet is printed, then the front side of the second sheet is printed after a printing time of one sheet, and then the back side of the first sheet that has been circulated is printed. Note that in this figure, the front side printing of the Kth sheet is represented by a black K on a white background, and the back side printing of the Kth sheet is represented by a white K on a black background.

After printing the back side of the first sheet, the front side of the third sheet is printed, and then the back side of the second sheet that has been circulated is printed. Thereafter, the front side of the newly fed print medium P and the back side of the circulated print medium P are printed alternately in the same manner. However, when the feeding of the new print medium P is completed at the end of printing, the back side of the circulated print medium is printed twice in succession with a printing time interval of one sheet between them, and then printing is completed. In this embodiment, the number of sheets of print medium P that are circulated between the end of printing on the front side of a given print medium P and the printing on the back side of that print medium P is defined as the number of sheets of paper in the transport path N, and in the case of FIG. 4(a), N=2.

When the inkjet printing device 1 performs single-sided printing, the time from the start of printing the first sheet to the start of printing the second sheet is assumed to be dt, as shown in FIG. 4(b). During single-sided printing, the print medium P can be fed one after another, so printing can be performed with maximum productivity of the printing unit 30 of the inkjet printing device 1. In other words, the print medium can be transported at a print speed and paper spacing (paper spacing) that the printing unit 30 can print at, within the range that maintains the required print quality, etc.

In contrast, when the inkjet printing device 1 performs double-sided printing, if double-sided printing can be performed with the same productivity as single-sided printing, that is, with the printing time dt per side, then double-sided printing will be performed with the maximum productivity of the inkjet printing device 1.

To achieve this productivity, when N=2, as shown in FIG. 4(a), for example, the first sheet of print medium P, which starts printing on its front side at time t11, will circulate and start printing on its back side at time t14, so it is sufficient to circulate the print medium P over a period of 3×dt.

However, since dt is determined by the size of the print medium P (the length of the print medium P in the transport direction), the paper gap, and the printing speed, when the printing speed is fast, 3 x dt can be shorter depending on the size of the print medium P. And in order to circulate the first sheet of print medium P within the time of 3 x dt, the motor driving the second double-sided transport roller 45 and other components may exceed their rated rotation speed. In such a case, if the paper feed interval is widened as shown in Figure 4 (c), the time of 3 x dt is lengthened and double-sided printing can be performed, but there is a problem of reduced productivity.

Therefore, in this embodiment, the productivity during double-sided printing is ensured and the motor of the second double-sided conveying roller 45 and the like are prevented from exceeding the rated rotation speed. Specifically, in this embodiment, the double-sided conveying speed is adjusted by changing the number of sheets N in the conveying path in the circulatory conveyance and the control conditions of the reversing unit 50. The double-sided conveying speed in the first embodiment is the conveying speed _V4 shown in Fig. 3, that is, the conveying speed of the constant speed conveying when the print medium P is conveyed in the reverse direction by the reversing roller 52.

When the number of sheets N on the transport path is increased, the number of sheets of print medium P present on the first double-sided transport path DS1 and the second double-sided transport path DS2 can be increased, and the above-mentioned double-sided transport speed _V4 can be slowed down. For example, the printing schedule for double-sided printing when the number of sheets N on the transport path is 2 is as shown in Fig. 4A as described above, but the printing schedule for double-sided printing when the number of sheets N on the transport path is 3 is as shown in Fig. 4D. In other words, the printing medium P only needs to be circulated for 5 x dt, and the double-sided transport speed _V4 can be slowed down.

In this embodiment, as control conditions for the inversion unit 50, the conveying speed _V3 when the print medium P is conveyed in the forward direction by the inversion rollers 52 to the inversion conveying path SR and the inversion unit wait time _SBwait described above are adjusted as necessary.

Specifically, when the number of sheets N in the transport path is increased as described above, the duplex transport speed _V4 can be slowed down, but as a result, the recalculated duplex transport speed _V4 may be slower than the printing speed (transport speed _V2 ). When the duplex transport speed _V4 is slower than the printing speed (transport speed _V2 ), inconvenience occurs. Specifically, for example, when the printing medium P is fed from the internal paper feed unit 20, the paper is fed from the internal paper feed unit 20 to the registration roller 14a at the same speed as the printing speed (transport speed _V2 ). Then, between feedings of the printing medium P from the internal paper feed unit 20, the printing medium P is supplied from the second duplex transport path DS2, and is controlled so that the printing medium P always reaches the registration roller 14a at a constant interval.

In this control, if the double-sided transport speed _V4 is slower than the printing speed (transport speed _V2 ), the transport speed between the vertical transport rollers 15 and the registration rollers 14a also slows down. On the other hand, since it is necessary to maintain the time at which the print medium P reaches the registration rollers 14a, the print medium P is transported toward the registration rollers 14a at an earlier timing. When the transport control of the print medium P is performed in this manner, as shown in FIG. 5, the rear end of the print medium P1 fed from the internal paper feed unit 20 may collide with the leading end of the print medium P2 supplied from the second double-sided transport path DS2.

Therefore, in order to avoid such collisions of the print medium P, when the double-sided transport speed _V4 becomes slower than the printing speed (transport speed _V2 ), the transport speed _V3 is slowed down so that the double-sided transport speed _V4 can be increased accordingly. Also, when the double-sided transport speed _V4 does not become equal to or faster than the printing speed (transport speed _V2 ) even when the transport speed _V3 is lowered, the reversing section wait time _SBwait is lengthened so that the double-sided transport speed _V4 can be increased accordingly.

In other words, in this embodiment, the productivity during double-sided printing is guaranteed, the motor of the second double-sided conveying roller 45 and the like are prevented from exceeding the rated rotation speed, and the double-sided conveying speed is adjusted by changing the number of sheets of paper N in the conveying path and the control conditions of the reversing unit 50 so that the double-sided conveying speed is equal to or faster than the printing speed.

Here, before specifically describing the method of adjusting the double-sided transport speed _V4 described above, a method of calculating the double-sided transport speed _V4 will be described with reference to Fig. 3. The numbers 1 to 5 shown at the top of Fig. 3 are numbers indicating each section within the range indicated by the arrow, with 1a to 1c indicating sections obtained by further dividing section 1, 3a to 3d indicating sections obtained by further dividing section 3, and 4a to 4e indicating sections obtained by further dividing section 4. In the following description, when a section number is added as a subscript to T, this refers to the transport time of the print medium P in the section with that number (except for section 5), and when a section number is added as a subscript to L, this refers to the transport distance of the print medium P in the section with that number.

First, the double-sided transport time T INV from the time t1 when the secondary paper feed unit 14 starts transporting the printing _medium P to the time when the printing medium P is circularly transported and refed by the secondary paper feed unit 14 again is calculated by the following formula (1).
T _INV = T ₁ + T ₂ + T ₃ + T ₄ + T ₅ ...(1)

₃ is calculated by the following formula (2): where _L1 is the distance from the registration roller 14a of the secondary paper feed unit 14 to the first belt platen roller 33.

₃ is calculated by the following formula (3): where _L2 is the distance from the first belt platen roller 33 to the reverse transport sensor RS plus the length of the print medium P.

₃ is calculated by the following formula (4). Note that _L3 is the distance from the reverse transport sensor RS to the reverse roller 52--the trailing end remaining amount Ls at the time of reverse transport. _T3d =SB _wait is the time for which the print medium P is temporarily stopped on the reverse transport path SR, and is initially set to an initial value.

₃ is calculated by the following formula (5): where _L4 is the distance from the reversing roller 52 to the registration roller - trailing end remaining amount Ls at the time of reversing + slack amount.

Moreover, time T5 in section 5 shown in FIG. ₃ is a waiting time until the registration rollers start to operate.

Then, by rearranging _T4 shown in the above formula (5), it can be expressed by the following formula (6).

Then, by substituting _T4 expressed by the above formula (6) into the above formula (1) and moving T _INV to the right-hand side, it can be expressed by the following formula (7).

By multiplying both sides of the above equation (7) by _V4 , a quadratic equation of _V4 as shown in the following equation (8) can be obtained. By solving the quadratic equation of equation (8), the double-sided conveying speed _V4 can be expressed by the following equation (9).

In addition, in order to ensure the same productivity rate as single-sided printing, T _INV in the above formula (9) needs to satisfy the following formula (10), just as the double-sided transport time needs to satisfy 3×dt when N=2 in FIG. 4A.
T _INV = {(length of print medium P/print speed) + sheet interval} (2 x number of sheets in path N-1)
...(10)

Next, a method for adjusting the above-mentioned double-sided conveying speed _V4 will be described with reference to the flow chart shown in FIG.

First, the control unit 60 provisionally determines the number of sheets N along the transport path in the circular transport based on the printing conditions (size (length) of the print medium P, printing speed, etc.) set by the user (S10). Specifically, the control unit 60 calculates the total transport path length La by adding the above-mentioned _L1 , _L2 , _L3 , and _L4 as shown in the following formula (11).
La=L ₁ +L ₂ +L ₃ +L ₄ ...(11)

In the case of double-sided transport, the print medium P on which the front side is printed and the print medium P on which the back side is printed are transported alternately, so it is assumed that two print media with a length equal to the sum of the length of the print medium P and the gap between the sheets are circulating, and the number of sheets N on the transport path is provisionally calculated using the following formula (12). The reason for provisionally calculating the number of sheets N on the transport path in this manner is that the number of sheets N on the transport path may be increased later. Note that, physically, the maximum number of sheets on the transport path is twice the number of sheets N on the transport path calculated using the following formula (12).
Number of sheets of paper in the transport path N=total transport path length La/{2×(length of print medium P+paper gap)}
...(12)

Then, when the control unit 60 provisionally calculates the number of sheets N on the transport path, it substitutes the provisionally calculated number of sheets N on the transport path into the above formula (9) to calculate the duplex transport speed _V4 (S12).

The control unit 60 checks whether the duplex conveying speed _V4 calculated in S12 can be calculated by the above formula (9) (S14). The duplex conveying speed _V4 is calculated by solving the quadratic equation shown in the above formula (8), but if the solution is an imaginary number, the control unit 60 determines that the duplex conveying speed _V4 cannot be calculated (S14, NO). Note that a case where the duplex conveying speed _V4 cannot be calculated means a case where the number of sheets N of the conveying path provisionally calculated in S10 cannot cause the print medium P conveyed in a circulatory manner to arrive at the registration roller 14a at a preset timing (a timing determined by the size of the print medium P, the printing speed, and the distance between the sheets).

Therefore, when the control unit 60 determines that the duplex conveying speed _V4 cannot be calculated (S14, NO), it changes the number of sheets N on the conveying path to N+1 (S16) and again substitutes the number of sheets N+1 into the above formula (9) to calculate the duplex conveying speed _V4 (S12). The control unit 60 repeats the increase in the number of sheets N on the conveying path (S16) and the calculation of the duplex conveying speed _V4 (S12) until the duplex conveying speed _V4 can be calculated. Note that the increase in the number of sheets N on the conveying path in S16 is for the purpose of making the duplex conveying speed _V4 calculable, and also for making the duplex conveying speed _V4 less than the maximum duplex conveying speed in the later determination in S18.

If the control unit 60 determines in S14 that the duplex conveying speed _V4 can be calculated (S14, YES), it compares the calculated duplex conveying speed _V4 with a preset maximum duplex conveying speed (S18). The maximum duplex conveying speed is a value calculated from the upper limit of the rated rotation speed of the motor that drives the rollers that convey the print medium P at the duplex conveying speed _V4 , such as the second duplex conveying roller 45.

If the double-sided transport speed _V4 is equal to or lower than the maximum double-sided transport speed in S18 (S18, NO), the control unit 60 judges whether the double-sided transport speed _V4 is equal to or higher than the printing speed (transport speed _V2 ) (S20). The reason for making the judgment in S20 is as described above.

If the double-sided transport speed _V4 is equal to or greater than the printing speed (transport speed _V2 ) (S20, YES), the control unit 60 calculates a reversing unit drive margin (S22). The reversing unit drive margin is set so that the next printing medium P transported toward the reversing unit 50 does not collide with the printing medium P being reversed in the reversing unit 50. The method of calculating the reversing unit drive margin will be described later.

Next, the control unit 60 judges whether the reversing unit driving margin is 20 ms or less (S24). If the reversing unit driving margin exceeds 20 ms (S24, NO), the control unit 60 determines that the double-sided conveying speed _V4 is appropriate and ends the adjustment process.

On the other hand, in S20, if the double-sided transport speed _V4 is less than the printing speed (transport speed _V2 ) (S20, NO), the control unit 60 checks whether the transport speed _V3 shown in Fig. 3 is equal to or greater than the printing speed (transport speed _V2 ) + 100 mm/s (S26). The transport speed V3 is the transport speed when the printed print medium P is fed into the reversing unit 50, and is the reversing unit forward rotation speed of the present invention. In addition, when the transport speed _V3 is the initial value, it is set to equal to or greater than the printing speed (transport speed _V2 ) + 100 mm/s.

Then, when the conveying speed _V3 is equal to or greater than the printing speed (conveying speed _V2 ) + 100 mm/s, the control unit 60 calculates the conveying speed _V3 - 100 mm/s, that is, reduces the conveying speed _V3 by 100 mm/s (S28), returns to S12, and recalculates the double-sided conveying speed _V4 by substituting the reduced conveying speed _V3 into the above formula (9).The control unit 60 then performs the processes from S14 onwards again.

Then, even if the control unit 60 recalculates the double-sided conveying speed _V4 while decreasing the conveying speed _V3 , if the double-sided conveying speed _V4 remains lower than the printing speed in S20, and as a result, the conveying speed _V3 becomes lower than the printing speed (conveying speed _V2 ) + 100 mm/s in S26 (NO in S26), the control unit 60 checks whether the conveying speed _V3 and the printing speed (conveying speed _V2 ) are different (S30). If the conveying speed _V3 and the printing speed (conveying speed _V2 ) are different (YES in S30), the control unit 60 sets the conveying speed _V3 to the same magnitude as the printing speed (conveying speed _V2 ) (S32). Then, the control unit 60 returns to S12 and recalculates the double-sided conveying speed _V4 by substituting the conveying speed _V3 that is the same magnitude as the printing speed (conveying speed _V2 ) into the above formula (9). Then, the control unit 60 performs the processes from S14 onwards again.

Then, if the results of the determinations in S18, S20, and S26 are NO again, or if the conveying speed _V3 is reduced in S28 and the conveying speed _V3 and the printing speed (conveying speed _V2 ) become the same in S30, the control unit 60 determines that the conveying speed _V3 and the printing speed (conveying speed _V2 ) are the same in S30 (S30, NO). In this case, since it is impossible to adjust the double-sided conveying speed _V4 by reducing the conveying speed _V3 , the control unit 60 lengthens the wait time _T3d = SB _wait shown in FIG. 3, which is the wait time of the reversing unit 50, by 1 ms (S34). Then, the control unit 60 returns to S12 and recalculates the double-sided conveying speed _V4 by substituting _T3 obtained by adding _T3d = SB _wait by 1 ms into the above formula (9). Then, the control unit 60 performs the process from S14 onwards again.

Then, in S20, the control section 60 repeats the above-mentioned process until the double-sided transport speed _V4 becomes equal to or greater than the printing speed (transport speed _V2 ). However, if it is determined in S18 that the double-sided transport speed _V4 exceeds the maximum double-sided transport speed (S18, YES), or if it is determined in S24 that the reversing section drive margin is equal to or less than 20 ms (S24, YES), then the control section 60 adds 1 ms to the paper interval, although this will result in reduced productivity, since the double-sided transport speed _V4 cannot be set appropriately by simply adjusting the transport speed _V3 and the reversing section wait time described above.

Then, the control unit 60 returns to S12 and substitutes T _INV, which is obtained by adding 1 ms to the sheet gap, into the above formula (9) to recalculate the duplex conveying speed _V4 . The control unit 60 then performs the processes from S14 onwards again. The control unit 60 repeats the addition of the sheet gap in S36 until it is determined in S20 that the duplex conveying speed _V4 is equal to or greater than the printing speed (conveying speed _V2 ) and that the reversing unit drive margin exceeds 20 ms.

Then, the control unit 60 terminates the processing at the point in S20 when it is determined that the double-sided conveying speed _V4 is equal to or greater than the printing speed (conveying speed _V2 ) and the reversing section drive margin exceeds 20 ms, and performs double-sided conveying control using the double-sided conveying speed _V4 , conveying speed _V3 , and reversing section wait time _T3d = SB _wait calculated at this point.

According to the inkjet printing device 1 of the above embodiment, the number of sheets N of the transport path for the printing medium P and the double-sided transport speed _V4 are calculated based on the size and printing speed of the printing medium P, and if the calculated double-sided transport speed _V4 exceeds the maximum double-sided transport speed or is less than the printing speed, the number of sheets N of the transport path and the control conditions of the reversing unit 50 are changed and the double-sided transport speed is recalculated. Therefore, it is possible to calculate the double-sided transport speed _V4 within a preset range (less than the maximum double-sided transport speed, and greater than or equal to the printing speed) without reducing the productivity of double-sided printing.

Furthermore, if the double-sided transport speed _V4 calculated based on the size and printing speed of the printing medium P is less than the printing speed (S20, NO in FIG. 6), the normal rotation speed of the reversing unit is reduced (S28 in FIG. 6) and the double-sided transport speed is recalculated. Therefore, as described above, the normal rotation speed of the reversing unit is reduced, and the double-sided transport speed _V4 can be increased by the amount corresponding to the reduction in the normal rotation speed of the reversing unit, thereby making it possible to avoid a collision between printing medium P1 and printing medium P2 as shown in FIG. 5.

In addition, if the double-sided conveying speed _V4 calculated by lowering the reverse rotation speed is the same as the reverse rotation speed (S30, NO in Figure 6), the reverse rotation wait time _T3d = SB _wait for the printing medium P in the reverse section 50 is lengthened (S34 in Figure 6) and the double-sided conveying speed _V4 is recalculated.Therefore, even if the reverse rotation speed cannot be lowered, the double-sided conveying speed _V4 can be increased by the amount of the lengthened reverse rotation wait time, thereby avoiding a collision between printing media P1 and printing media P2 as shown in Figure 5.

In other words, in the inkjet printing device 1 of this embodiment, by adding the number N of sheets of paper in the transport path, slowing down the forward rotation speed of the inversion unit 50, and changing the inversion unit wait time as described above, it is possible to make the double-sided transport speed _V4 less than the maximum double-sided transport speed and equal to or greater than the printing speed without increasing the space between the sheets, thereby avoiding the collision between printing medium P1 and printing medium P2 as shown in Figure 5.

Furthermore, in this embodiment, a driving margin for the inversion unit is also secured, so that collisions of the print medium P at the inversion unit 50 can also be avoided.

Therefore, the inkjet printing device 1 of this embodiment can maintain productivity without causing transport problems.

Regarding productivity, for example, if the paper gap for single-sided printing is 100 ms, in the conventional method the paper gap must be increased to 200 ms for double-sided printing, but with the inkjet printing device of this embodiment, the paper gap can be maintained at 100 ms by changing the number of sheets of paper N in the transport path and the control conditions of the reversing unit 50.

In addition, in the inkjet printing device 1 of the above embodiment, the reversing section forward rotation speed (transport speed _V3 ) and the reversing section wait time are adjusted as described above, but the reversing section forward rotation speed is adjusted before the reversing section wait time. By giving priority to decelerating the reversing section forward rotation speed in this manner, the acceleration time can be shortened, and the transport of the print medium P can be stabilized. Furthermore, vibration and power consumption can be suppressed by reducing the reversing section forward rotation speed.

In the inkjet printing apparatus 1 of the above embodiment, the double-sided conveying speed _V4 is adjusted before the reverse rotation speed (conveying speed _V3 ). This is because the conveying distance at the double-sided conveying speed _V4 is longer than the conveying distance at the reverse rotation speed, which allows for a wider range of adjustment.

Next, a method for calculating the above-mentioned inversion unit drive margin will be described. The inversion unit drive margin is set so that the next print medium P transported toward the inversion unit 50 does not collide with the print medium P while it is being inverted in the inversion unit 50 as described above.

First, calculate the interval at which the print medium P transported from the printing unit 30 enters the inversion unit 50 (paper inversion interval). The time required for printing in the printing unit 30 can be calculated by dividing the length of the print medium P by the printing speed, and the paper feed interval for the printing unit 30 can be calculated by adding the time required for printing to the paper interval.

Since the printed printing media P enter the inversion unit 50 at intervals of one out of two sheets, the paper inversion entry interval into the inversion unit 50 is twice the time of the paper feed interval of the printing unit 30. Therefore, the paper inversion entry interval Tnp is calculated by the following formula (13).
Tnp={(length of printing medium P/printing speed)+paper interval}×2 (13)

On the other hand, the operation time T _SB of the reversing rollers 52 of the reversing unit 50 is T _SB =T ₃ +T ₄ .

In order to prevent the next printing medium P from colliding while the printing medium P is being reversed, the relationship between _TSB and Tnp must be _TSB < _Tnp . Therefore, the reversing section drive margin can be calculated by _Tnp - TSB. In S24 shown in Fig. 6, it is determined whether _Tnp - _TSB is 20 _ms or less.

Next, in the first embodiment described above, when adjusting the double-sided transport speed _V4 according to the flowchart of FIG. 6, a preset paper interval is used when calculating the double-sided transport speed _V4 based on the above equations (9) and (10). However, when a post-processing device is connected to the inkjet printing apparatus 1, for example, this paper interval needs to take into account the time required for post-processing performed in the post-processing device.

Specifically, for example, in a post-processing device, when performing alignment processing as post-processing for each print medium P discharged from the inkjet printing device 1, it is necessary to adjust the paper spacing so that the next print medium P is discharged after the alignment processing for the previously discharged print medium P is completed.

Therefore, a method for adjusting the duplex conveying speed _V4 in consideration of the sheet interval according to the time required for the post-processing will be described below with reference to the flowchart shown in Fig. 7. Note that the following description will focus on points that are different from the process in the flowchart shown in Fig. 6.

First, the control unit 60 provisionally determines the number of sheets of paper N along the transport path in the circular transport based on the printing conditions (such as the size (length) of the print medium P and the printing speed) set by the user, as in the above embodiment (S40).

Specifically, the number of sheets N on the transport path is provisionally calculated based on the above formula (12), and in this case, the shortest sheet spacing corresponding to the time required for post-processing is substituted as the sheet spacing. The sheet spacing corresponding to the time required for post-processing may be preset in the inkjet printing device 1, or the time required for post-processing may be obtained from a post-processing device connected to the inkjet printing device 1, and the spacing may be calculated based on the obtained time required for post-processing, the size of the print medium P, and the printing speed.

Then, the control unit 60 calculates the duplex conveying speed _V4 by substituting the provisionally calculated number of sheets N in the conveying path into the above formulas (9) and (10) in the same manner as in the above embodiment (S42), but at this time, the shortest sheet interval corresponding to the time required for the above-mentioned post-processing is used as the sheet interval to be substituted into the formula (10). Then, the subsequent processes from S44 to S60 are the same as the processes from S14 to S30 in the flowchart shown in FIG.

Then, even if the control unit 60 recalculates the double-sided conveying speed _V4 while lowering the conveying speed _V3 (reversal unit forward rotation speed), if the double-sided conveying speed _V4 remains less than the printing speed in S50 and the conveying speed _V3 cannot be lowered any further in relation to the printing speed, that is, if it is determined in S60 that the conveying speed _V3 and the printing speed are the same (S60, NO), the control unit 60 proceeds to a step of adjusting the wait time of the reversal unit 50 as in the above embodiment.

Then, the control unit 60 checks whether the _waiting time SBwait of the inversion unit 50 is equal to or shorter than the shortest sheet interval corresponding to the time required for post-processing (S64). Note that hereinafter, the shortest sheet interval corresponding to the time required for post-processing is referred to as the post-processing required shortest sheet interval. The reason for comparing the waiting time SBwait with the post-processing required shortest sheet interval in this manner is that if the waiting time SBwait is longer than the post-processing required shortest sheet interval, the next printing medium P will collide with the printing medium P that has stopped temporarily in the inversion unit 50.

Then, in S64, if it is determined that the wait time SB _wait is equal to or shorter than the post-processing required shortest paper interval, the control unit 60 lengthens the wait time SB _wait by 1 ms (S66).Then, the control unit 60 returns to S42 and substitutes _T3, which is obtained by adding 1 ms to _T3d = SB _wait , into the above formula (9) to recalculate the duplex conveying speed _V4.Then , the control unit 60 performs the processes from S44 onwards again.

Then, in S50, the control unit 60 repeats the above-mentioned process until the duplex transport speed _V4 becomes equal to or greater than the printing speed (transport speed _V2 ). If it is determined in S64 that the _wait time SBwait is longer than the required minimum paper interval for post-processing, the control unit 60 checks whether the required minimum paper interval for post-processing is 200 ms or less (S68). Note that 200 ms is the longest paper interval that is allowable in the inkjet printing device 1, and is a preset value. This value differs depending on the configuration of the inkjet printing device 1, and is not limited to 200 ms.

Then, when the control section 60 determines in S68 that the post-processing required shortest paper interval is 200 ms or less (S68, YES), it adds 1 ms to the paper interval, although this will result in a decrease in productivity, since it is not possible to appropriately set the double-sided conveying speed _V4 by simply adjusting the conveying speed _V3 and the reversing section wait time described above (S72).

Then, the control unit 60 returns to S42 and calculates the duplex conveying speed _V4 based on the formula (9) and the above formula (10) (S42), but at this time, the post-processing required shortest paper interval is used as the paper interval to be substituted into the formula (10). Next, the control unit 60 performs the processes from S44 onwards again.

The control section 60 repeatedly adds the sheet interval in S72 until it is determined in S50 that the duplex conveying speed _V4 is equal to or greater than the printing speed (conveying speed _V2 ) and the reversing section drive margin exceeds 20 ms.

On the other hand, if the control unit 60 determines, as a result of repeating the addition of the sheet gap in S72, that the duplex transport speed _V4 is equal to or greater than the printing speed (transport speed _V2 ) and before it determines that the reversing unit drive margin exceeds 20 ms, the sheet gap after the addition exceeds 200 ms in S68 (S68, NO), it changes the number of sheets on the transport path N to N+1 (S70), again substitutes the number of sheets on the transport path N+1 into the above formula (10), and calculates the duplex transport speed _V4 based on the above formula (9) (S42).The control unit 60 then performs the processes from S44 onwards again.

Note that even if the control unit 60 determines in S48 that the duplex conveying speed _V4 calculated in S44 exceeds the maximum duplex conveying speed (S48, YES), or determines in S54 that the reversing unit drive margin is 20 ms or less (S54, YES), the process from S68 onwards is repeated because the duplex conveying speed _V4 cannot be set appropriately by simply adjusting the conveying speed _V3 and the reversing unit wait time described above.

Then, the control unit 60 terminates processing at the point in S50 when it is determined that the double-sided conveying speed _V4 is equal to or greater than the printing speed (conveying speed _V2 ) and the reversing section drive margin exceeds 20 ms, and performs double-sided conveying control using the double-sided conveying speed _V4 , conveying speed _V3 , reversing section wait time _T3d = SB _wait , and paper spacing calculated at this point.

7, the duplex transport speed _V4 can be adjusted in consideration of the paper interval corresponding to the time required for post-processing. That is, the paper can be discharged from the inkjet printing apparatus 1 to the post-processing apparatus at a timing corresponding to the paper interval, and the duplex transport speed _V4 can be adjusted to within a preset range (less than the maximum duplex transport speed and equal to or greater than the printing speed) without reducing the productivity of _duplex printing.

Furthermore, if the double-sided conveying speed _V4 calculated based on the size of the printing medium P, the printing speed, and the minimum paper interval required for post-processing is less than the printing speed (S50, NO in FIG. 7), the normal rotation speed of the reversing unit (conveying speed _V3 ) is reduced (S58 in FIG. 7) and the double-sided conveying speed _V4 is recalculated. Therefore, as described above, the normal rotation speed of the reversing unit is reduced, and the double-sided conveying speed _V4 can be increased by the amount, thereby making it possible to avoid a collision between printing medium P1 and printing medium P2 as shown in FIG. 5.

Furthermore, if the double-sided transport speed _V4 calculated by lowering the forward rotation speed (transport speed _V3 ) of the reversing unit is less than the printing speed, the stop time of the printing medium P in the reversing unit 50 is changed within the range of the shortest paper interval required for post-processing, and the double-sided transport speed V4 is recalculated, thereby making it possible to avoid collisions of the printing medium P in the reversing unit 50.

Next, an inkjet printing device 2 using a second embodiment of the double-sided printing device of the present invention will be described. In the inkjet printing device 1 of the first embodiment, as shown in FIG. 1, the inversion unit 50 is provided at the bottom of the inkjet printing device 1, and the print medium P inverted by the inversion unit 50 is transported to the registration unit 1 via the second double-sided transport path DS2. In the inkjet printing device 2 of the second embodiment, as shown in FIG. 8, the inversion unit 150 is disposed on the upper side, and the print medium P inverted by the inversion unit 150 is transported directly to the registration unit 114. The inkjet printing device 2 of the second embodiment will be specifically described below. Note that the up, down, left, and right directions shown in FIG. 8 are the up, down, left, and right directions of the inkjet printing device 2 of the second embodiment. Also, the front side of the paper in FIG. 8 is the front direction, and the back side of the paper is the rear direction.

As shown in FIG. 8, the inkjet printing device 2 of this embodiment includes a side paper feed unit 110, an internal paper feed unit 120, a printing unit 130, a paper discharge unit 140, and an inversion unit 150.

The printing unit 130 and the internal paper feed unit 120 are housed and installed in a housing made of metal or resin. The side paper feed unit 110 and the paper discharge unit 140 are installed with a part of them housed within the housing and a part protruding outside the housing.

The side paper feed unit 110 includes a paper feed tray 111 on which the print medium P is placed, a primary paper feed unit 112 that feeds and transports only the topmost print medium P from the paper feed tray 111, and a secondary paper feed unit 114 that sends the print medium P transported by the primary paper feed unit 112 to the printing unit 130 at a predetermined timing.

The primary paper feed unit 112 includes a paper feed roller and a paper feed motor that drives the paper feed roller.

The secondary paper feed unit 114 includes a registration roller 114a that is contacted by the leading edge of the print medium P transported from the primary paper feed unit 112 or the print medium P transported from the internal paper feed unit 120, stops the print medium P temporarily, forming slack, thereby correcting skew, and a registration motor that drives the registration roller 114a. In this embodiment, the secondary paper feed unit 114 corresponds to the registration unit of the present invention.

The internal paper feed unit 120 includes a paper feed tray 121a on which the print medium P is placed, a primary paper feed unit 122a that feeds only the topmost print medium P from the paper feed tray 121a and transports it onto the paper feed transport path FR, a paper feed tray 121b on which the print medium P is placed, a primary paper feed unit 122b that feeds only the topmost print medium P from the paper feed tray 121b and transports it onto the paper feed transport path FR, a paper feed tray 121c on which the print medium P is placed, a primary paper feed unit 122c that feeds only the topmost print medium P from the paper feed tray 121c and transports it onto the paper feed transport path FR, and vertical transport rollers 115.

The primary paper feed units 122a, 122b, and 122c are equipped with paper feed rollers and paper feed motors that drive the paper feed rollers.

The printing medium P fed from the paper feed tray 121a by the primary paper feed unit 122a and the printing medium P fed from the paper feed tray 121b by the primary paper feed unit 122b are transported toward the vertical transport roller 115.

The vertical conveying rollers 115 are provided on the conveying path between the registration rollers 114a and the primary paper feed sections 122a, 122b, and 122c.

In this way, the print medium P is transported to the secondary paper feed section 114 from the side paper feed section 110 or the internal paper feed section 120, and also from the inversion section 150 described below.

Therefore, just before the secondary paper feed unit 114 in the transport direction, there is a junction where the transport path of the print medium P fed from the side paper feed unit 110 or the internal paper feed unit 120 and the transport path of the print medium P with one side printed and transported from the inversion unit 150 join together. Based on this junction, the path on the paper feed mechanism side is called the paper feed transport path FR, and the other path is called the circulating transport path CR.

In addition, a number of paper detection sensors that detect the print medium P are provided on the circulating transport path CR, and the transport of the print medium P is controlled by the control unit 160, which will be described later, based on the detection signals detected by the paper detection sensors.

The printing unit 130, like the first embodiment, includes four line heads 131, a circular conveyor belt 132 arranged opposite the line heads 131, a first belt platen roller 133, and a second belt platen roller 134.

The conveyor belt 132 is formed from a circular endless belt and has many suction holes formed therein. The print medium P fed from the secondary paper feed unit 114 is conveyed to the circular conveyor belt 132. The print medium P is then adsorbed onto the conveyor belt 132 by the suction of a suction fan (not shown) installed on the back side of the conveyor path surface of the conveyor belt 132, and is conveyed at a predetermined conveying speed. Then, while the print medium P is conveyed by the conveyor belt 132, ink is ejected from the line head 131 onto the print medium P, thereby performing a printing process on the print medium P.

A conveyor belt 132 is stretched across the first belt platen roller 133 and the second belt platen roller 134, and the first belt platen roller 133 and the second belt platen roller 134 are driven by a conveyor motor (not shown), causing the conveyor belt 132 to rotate clockwise in FIG. 1.

The configuration of each line head 131 is the same as that of each line head 31 in the first embodiment.

The print medium P printed by the printing unit 130 is transported on the circulatory transport path CR by transport rollers and the like arranged on the circulatory transport path CR. On the circulatory transport path CR, a switching mechanism 143 is provided which switches between guiding the print medium P transported on the circulatory transport path CR to the paper discharge unit 140 or recirculating it on the circulatory transport path CR. Specifically, the switching mechanism 143 switches between the transport path on the paper discharge unit 140 side and the transport path on the inversion unit 150 side.

The paper discharge section 140 has a tray-shaped paper discharge stand 141 that protrudes from the housing of the inkjet printing device 1, and a pair of paper discharge rollers 142 that discharge the print medium P onto the paper discharge stand 141. The print medium P guided toward the paper discharge section 140 by the switching mechanism 143 is then discharged onto the paper discharge stand 141 by the paper discharge rollers 142.

The inversion unit 150 includes an inversion table 151 having an inversion transport path SR that inverts the print medium P, an inversion roller 152 that transports the print medium P from the circulatory transport path CR to the inversion table 151 and returns the print medium P transported to the inversion table 151 back onto the circulatory transport path CR, and an inversion motor (not shown) that drives the inversion roller 152.

The printing medium P guided to the inversion unit 150 by the switching mechanism 143 is transported from the circulating transport path CR to the inversion table 151 by the inversion rollers 152, and then returned from the inversion table 151 to the circulating transport path CR, so that the printing medium P is transported on the circulating transport path CR in an inverted state. The inverted printing medium P is then transported again toward the printing unit 130 by multiple rollers, such as the transport rollers 153, provided on the circulating transport path CR.

The print medium P transported by the transport roller 153 is transported again to the registration roller 114a of the secondary paper feed unit 114, and is sent out again toward the printing unit 130 at a predetermined timing by the registration roller 114a. Then, the printing unit 130 applies printing processing to the back side of the print medium P.

Figure 9 is a block diagram showing the schematic configuration of the control system of the inkjet printing device 2 of this embodiment. As shown in Figure 9, the inkjet printing device 2 of the second embodiment also includes a control unit 160 and an operation panel 170.

The control unit 160 controls the entire inkjet printing device 2 and includes a CPU (Central Processing Unit) and a semiconductor memory. The control unit 160 controls the operation of each part of the inkjet printing device 2 by having the CPU execute a program that is pre-stored in the semiconductor memory.

In addition, the control unit 160 acquires image data output from a computer or image data read by a scanner, and performs printing processing by controlling the printing unit 130 based on the image data.

The control unit 160 also acquires printing conditions such as the size and printing speed of the print medium P, and performs processes such as calculating the double-sided transport speed of the print medium P, which will be described later, and calculating the number of sheets of paper along the transport path of the print medium P, based on the printing conditions.

Next, the transport operation of the print medium P of the inkjet printing device 2 of this embodiment will be described with reference to the timing chart shown in FIG. 10. Note that the horizontal axis of FIG. 10 represents time, and the vertical axis represents the transport speed of the print medium P. Also, the transport operation during double-sided printing will be described here.

First, the leading edge of the print medium P transported by the side feeder 110 or the internal feeder 120 comes into contact with the registration roller 114a, and the medium stops once a slack is formed.

Then, at time t1, the print medium P is transported by the registration rollers 114a toward the printing unit 130. At this time, the secondary paper feed unit 114 accelerates at an acceleration α1, and then transports the print medium P at a transport speed _V1 .

Then, the secondary paper feed unit 114 subsequently decelerates at a deceleration rate α2, and at time t2 when the conveying speed reaches _V2, delivers the print medium P to the conveying belt 132. Note that the relationship between the conveying speed _V1 and the conveying speed _V2 is _V1 > _V2 , as shown in FIG. 10. This allows the gap between the sheets to be narrowed.

The conveyor belt 132 is also driven at a conveying speed _V2 , and conveys the printing medium P received from the secondary paper feed unit 114 at a constant speed of conveying speed _V2 . Then, the printing unit 130 performs a printing process on the front side of the printing medium P conveyed at conveying speed _V2 . Then, from time t3 when the rear end of the printing medium P leaves the conveyor belt 132, the printing medium P accelerates at an acceleration rate α3, and conveys the printing medium P at a constant speed of conveying speed _V3 on the circulating conveying path CR. Next, the printing medium P is guided to the reverse conveying path SR by conveyance by the reversing rollers 152.

After the print medium P is guided to the reverse transport path SR, the reverse roller 152 decelerates at a deceleration rate α4 to stop the print medium P by switching back. Then, when the rear end of the print medium P reaches a position that is a distance Ls (amount of rear end remaining when reversing) away from the reverse roller 152, the reverse roller 152 stops (time t4).

The trailing end remaining amount Ls during reversal is set in advance as a distance at which the printing medium P can be sufficiently drawn into the reversing transport path SR so that it can be reversed, and at which the printing medium P can be transported in both directions without coming off the reversing rollers 152. For this reason, the deceleration start position of the reversing rollers 152 is a position at which the trailing end of the printing medium P can stop at a position the distance Ls from the reversing rollers 152 when it is decelerated from the transport speed _V3 at the deceleration rate α4.

Then, at time t5, which is the reversing section wait time from time t4 when the transport of the print medium P by the reversing rollers 152 is temporarily stopped, the reversing rollers 152 resume rotation in the reverse direction, and the print medium P is switched back and transported. The reversing section wait time SB _wait from time t4 to time t5 is initially set to an initial value, but is changed as necessary when calculating the duplex transport speed, which will be described later.

Then, after the print medium P starts to be reversed, the print medium P is accelerated at an acceleration α5 and transported by the reversing rollers 152. When the print medium P reaches the transport speed _V3 again, it is transported at the constant speed by the reversing rollers 152 and the transport rollers 153.

Thereafter, in order to stop the printing medium P at the registration rollers 114a, the reversing rollers 152 and the transport rollers 153 decelerate at a deceleration rate α6. In this embodiment, the printing medium P is transported at a constant speed at transport speed _V4 while being decelerated at deceleration rate α6. In this way, by transporting the printing medium P at a constant speed once before the leading edge of the printing medium P abuts against the registration rollers 114a of the secondary paper feed unit 114, the speed at which the printing medium P collides with the registration rollers 114a can be slowed down, and the collision sound can be reduced. However, it is not necessary to provide this constant speed transport period.

Furthermore, the deceleration start position of the reversing roller 152 and the transport roller 153 described above may be a position where the leading edge of the print medium P can stop in the secondary paper feed unit 114 when the print medium P is decelerated from the _transport speed V3 at the deceleration rate α6. However, in the secondary paper feed unit 114, the print medium P comes into contact with the secondary paper feed unit 114 once to correct the skew as described above, so the print medium P stops with some slack. The amount of slack formed during the skew correction is set in advance.

Then, at time t7, which is a preset registration start waiting time from time t6 when the transport of the print medium P by the reversing roller 152 and the transport roller 153 stops, the registration roller 114a starts to rotate, and the print medium P is sent out towards the printing unit 130.

Then, the operation from time t1 shown in FIG. 10 is repeated, and the back side is printed by the line head 131 while the transport belt 132 transports the sheet at a constant transport speed _V2 .

The print medium P with the back side printed is guided to the paper discharge tray 141 by the switching mechanism 143, and is discharged by the paper discharge rollers 142 at a transport speed suitable for paper discharge.

Next, we will explain the printing schedule for double-sided printing in the inkjet printing device 2 of the second embodiment.

In the inkjet printing apparatus 1 of the first embodiment described above, the double-sided conveying speed is adjusted by changing the number of sheets N in the conveying path in the circulatory conveyance and the control conditions of the inverting unit 50 so as to ensure productivity during double-sided printing and prevent the motor of the second double-sided conveying roller 45 from exceeding the rated rotation speed, but the basic idea is the same in the second embodiment, and the number of sheets N in the conveying path and the control conditions of the inverting unit 150 are changed to adjust the double-sided conveying speed so as to ensure productivity during double-sided printing and prevent the motor of the conveying roller on the circulatory conveying path RS from exceeding the rated rotation speed. In this embodiment, the conveying speed _V3 shown in FIG. 10 corresponds to the double-sided conveying speed of the present invention.

When the number N of sheets on the transport path is increased, the number of print media P on the circulating transport path RS can be increased, so that the transport speed _V3 shown in FIG. 10 can be slowed down.

In this embodiment, the inverter wait time SB _wait described above is adjusted as necessary as a control condition for the inverter 150 .

Specifically, when the number of sheets N in the transport path is increased as described above, the transport speed _V3 can be slowed down, but as a result, the recalculated transport speed _V3 may be slower than the printing speed (transport speed _V2 ). When the transport speed _V3 is slower than the printing speed (transport speed _V2 ), inconvenience occurs. Specifically, for example, when the printing medium P is fed from the internal paper feed unit 120, the paper is fed from the internal paper feed unit 120 to the registration roller 114a at the same speed as the printing speed (transport speed _V2 ). Then, between feedings of the printing medium P from the internal paper feed unit 120, the printing medium P is supplied from the inversion unit 150 via the circulating transport path CR, and is controlled so that the printing medium P always reaches the registration roller 114a at a constant interval.

In this type of control, if the transport speed _V3 is slower than the printing speed (transport speed _V2 ), the transport speed between the inversion unit 150 and the registration rollers 114a also slows down. On the other hand, since it is necessary to maintain the time at which the print medium P reaches the registration rollers 114a, the print medium P is transported toward the registration rollers 114a at an earlier timing. When the transport control of the print medium P is performed in this manner, the rear end of the print medium P fed from the internal paper feed unit 120 may collide with the front end of the print medium P transported from the inversion unit 150.

Therefore, in order to avoid such collision of the printing medium P, when the transport speed _V3 becomes slower than the printing speed (transport speed _V2 ), the reversing section wait time _SBwait is lengthened so that the transport speed _V3 can be made faster by that amount.

That is, in this embodiment, productivity during double-sided printing is ensured, and the motors of the transport rollers on the circulating transport path CR do not exceed their rated rotation speeds. Furthermore, the number of sheets of paper in the transport path N and the control conditions of the reversing unit 50 are changed to adjust the transport speed _V3 so that the transport speed _V3 is equal to or greater than the printing speed.

The basic concept of the method for calculating the conveying speed _V3 is the same as that of the method for calculating the double-sided conveying speed _V4 in the first embodiment, and the conveying speed _V3 is calculated based on the timing chart shown in Fig. 10. Specifically, the conveying speed V3 is calculated by the following formula (14).

10, like Fig. 3, the numbers 1 to 5 shown at the top indicate the sections within the range of the arrows, with 1a to 1c indicating sections obtained by further dividing section 1, 3a to 3d indicating sections obtained by further dividing section 3, and 4a to 4e indicating sections obtained by further dividing section 4. When a section number is added as a subscript to T, it refers to the transport time of the print medium P in the section with that number (except for section 5), and when a section number is added as a subscript to L, it refers to the transport distance of the print medium P in the section with that number.

In order to ensure a productivity rate equivalent to that of single-sided printing, T _INV in the above formula (14) must satisfy the following formula (15).
T _INV = {(length of print medium P/print speed) + sheet interval} (2 x number of sheets in path N-1)
...(15)

Next, a method for adjusting the above-mentioned conveying speed _V3 will be described with reference to the flowchart shown in Fig. 11. Note that, here, a method for adjusting the conveying speed _V3 will be described taking into consideration the sheet interval according to the time required for the above-mentioned post-processing.

First, the control unit 160 provisionally determines the number of sheets of paper N along the transport path in the circulating transport path CR based on the printing conditions (size (length) of the print medium P, printing speed, etc.) set by the user (S80). Specifically, the control unit 160 provisionally calculates the number of sheets of paper N along the transport path according to the above formula (12). Note that in the second embodiment, the total transport path length La is L1+L2+L3+L4 as shown in FIG. 10.

Then, when the control unit 160 provisionally calculates the number of sheets N on the transport path, it substitutes the provisionally calculated number of sheets N on the transport path into the above formulas (14) and (15) to calculate the duplex transport speed _V3 (S82).

The control unit 160 checks whether the duplex conveying speed _V3 calculated in S82 can be calculated by the above formula (14) (S84). The duplex conveying speed _V3 is calculated by solving the quadratic equation shown in the above formula (14), but if the solution is an imaginary number, the control unit 160 determines that the duplex conveying speed _V3 cannot be calculated (S84, NO). Note that a case where the duplex conveying speed _V3 cannot be calculated means a case where the number of sheets N of the conveying path temporarily calculated in S80 is such that the print medium P conveyed in a circulatory manner cannot arrive at the registration roller 114a at a preset timing (a timing determined by the size of the print medium P, the printing speed, and the distance between the sheets).

Therefore, when the control unit 160 determines that the duplex conveying speed _V3 cannot be calculated (S84, NO), it changes the number of sheets N on the conveying path to N+1 (S86) and again substitutes the number of sheets N+1 into the above formula (14) to calculate the duplex conveying speed _V3 (S82). The control unit 160 repeats the increase in the number of sheets N on the conveying path (S86) and the calculation of the duplex conveying speed _V3 (S82) until the duplex conveying speed _V3 can be calculated. Note that the increase in the number of sheets N on the conveying path in S86 is for the purpose of making the duplex conveying speed _V3 calculable, and also for making the duplex conveying speed _V3 less than the maximum duplex conveying speed in the later determination in S88.

If the control unit 160 determines in S84 that the duplex transport speed _V3 can be calculated (S84, YES), it compares the calculated duplex transport speed _V3 with a preset maximum duplex transport speed (S88). The maximum duplex transport speed is a value calculated from the upper limit of the rated rotation speed of the motor that drives the rollers that transport the print medium P at the duplex transport speed _V3 .

If the duplex conveying speed _V3 is equal to or lower than the maximum duplex conveying speed in S88 (S88, NO), the control unit 160 judges whether the duplex conveying speed _V3 is equal to or higher than the printing speed (conveying speed _V2 ) (S90). The reason for making the judgment in S90 is as described above.

If the double-sided conveying speed _V3 is equal to or greater than the printing speed (conveying speed _V2 ) (S90, YES), the control section 160 calculates a reverse section driving margin (S92).

Next, the control unit 160 judges whether the reversing unit driving margin is 20 ms or less (S94). If the reversing unit driving margin exceeds 20 ms (S94, NO), the control unit 160 determines that the duplex conveying speed _V3 is appropriate and ends the adjustment process.

On the other hand, in S90, if the double-sided conveying speed _V3 is less than the printing speed (conveying speed _V2 ) (S90, NO), the control unit 160 proceeds to a step of adjusting the wait time of the inversion unit 150, and at this time, it checks whether the wait time SB _wait of the inversion unit 50 is less than or equal to the shortest paper interval required for post-processing (S96).

Then, in S96, if it is determined that the wait time SB _wait is equal to or shorter than the minimum sheet interval required for post-processing (S96, YES), the wait time SB _wait is lengthened by 1 ms (S98). Then, the control unit 160 returns to S82 and recalculates the duplex conveying speed _V3 by substituting the time obtained by adding the wait time SB _wait by 1 ms into the above formula (14). Then, the control unit 160 performs the process from S84 onwards again. By lengthening the wait time SB _wait in this way, the duplex conveying speed _V3 can be increased, so that it is possible to avoid collision between the rear end of the printing medium P fed from the internal paper feed unit 120 and the front end of the printing medium P conveyed from the reversing unit 150. Also, by adding the wait time SB _wait within the range of the minimum sheet interval required for post-processing as described above, it is possible to avoid collision of the printing medium P in the reversing unit 150.

Then, in S90, the control unit 160 adds 1 ms to the wait time SB _wait as described above until the duplex transport speed _V3 becomes equal to or greater than the printing speed (transport speed _V2 ). If the wait time SB _wait after the addition becomes longer than the required minimum paper interval for post-processing in S96 (S96, NO), the control unit 160 checks whether the required minimum paper interval for post-processing is 200 ms or less (S100). Note that 200 ms is the longest paper interval that is allowable in the inkjet printing device 2 and is a preset value. This value differs depending on the configuration of the inkjet printing device 2 and is not limited to 200 ms.

Then, when the control unit 160 determines in S100 that the post-processing required shortest paper interval is 200 ms or less (S100, YES), the control unit 160 adds 1 ms to the paper interval, although this will result in a decrease in productivity, since the duplex conveying speed _V3 cannot be set appropriately by simply adjusting the wait time SB _wait described above.

Then, the control unit 160 returns to S82 and calculates the duplex conveying speed _V3 based on the formula (14) and the above formula (15) (S82), but at this time, the post-processing required shortest paper interval is used as the paper interval to be substituted into the formula (15). Next, the control unit 160 performs the processes from S84 onwards again.

The control unit 160 repeatedly adds the paper interval in S104 until it is determined in S90 that the duplex conveying speed _V3 is equal to or greater than the printing speed (conveying speed _V2 ) and the reversing unit drive margin exceeds 20 ms.

On the other hand, if the control unit 160 determines, as a result of repeating the addition of the sheet gap in S104, that the duplex conveying speed _V3 is equal to or greater than the printing speed (conveying speed _V2 ) and that the post-processing required shortest sheet gap exceeds 200 ms in S100 before it determines that the reversing unit drive margin exceeds 20 ms (S100, NO), it changes the number of sheets N on the conveying path to N+1 (S102), again substitutes the number of sheets N+1 on the conveying path into the above formula (15), and calculates the duplex conveying speed _V3 based on formula (14) (S82).The control unit 160 then performs the processes from S84 onwards again.

Incidentally, even if it is determined in S88 that the duplex conveying speed _V3 exceeds the maximum duplex conveying speed (S88, YES), or if it is determined in S94 that the reversing section drive margin is 20 ms or less (S94, YES), the above-mentioned adjustment of the reversing section wait time _SBwait alone is not enough to set the duplex conveying speed _V3 appropriately, and the processing from S100 onwards is repeated.

Then, the control unit 160 ends the processing at the point in time when it is determined in S90 that the double-sided conveying speed _V3 is equal to or greater than the printing speed (conveying speed _V2 ) and that the reversing unit drive margin exceeds 20 ms, and performs double-sided conveying control using the double-sided conveying speed _V3 , the reversing unit wait time _SBwait , and the paper spacing calculated at this point.

The above embodiment is an example in which the double-sided printing device of the present invention is applied to an inkjet printing device, but the printing method is not limited to the inkjet method, and the double-sided printing device of the present invention may also be applied to a laser method or a stencil printing method printing device.

The following supplementary notes are further disclosed regarding the double-sided printing device of the present invention.
(Additional Note)

In the double-sided printing device of the present invention, the control unit can change the control conditions of the inversion unit and recalculate the double-sided transport speed if the double-sided transport speed calculated based on the size of the print medium and the printing speed is less than the printing speed.

In addition, in the double-sided printing device of the present invention, if the double-sided transport speed calculated based on the size of the print medium and the printing speed is less than the printing speed, the control unit can reduce the forward rotation speed of the inversion unit when the printed print medium is fed into the inversion unit, and recalculate the double-sided transport speed.

In addition, in the double-sided printing device of the present invention, if the double-sided transport speed calculated by lowering the forward rotation speed of the inversion unit is less than the printing speed, the control unit can change the stop time of the print medium in the inversion unit and recalculate the double-sided transport speed.

In addition, in the double-sided printing device of the present invention, if the double-sided transport speed calculated based on the size of the print medium and the printing speed is less than the printing speed, the control unit can change the stop time of the print medium in the inversion unit and recalculate the double-sided transport speed.

In addition, in the duplex printing device of the present invention, the control unit can calculate the number of sheets of print media in the print media transport path and the duplex transport speed when circulating and re-feeding the printed print media to the registration unit based on the size of the print media, the printing speed, and the paper spacing according to the time required for post-processing in the post-processing device connected to the duplex printing device.

In addition, in the double-sided printing device of the present invention, if the double-sided transport speed calculated based on the paper spacing corresponding to the size of the print medium, the printing speed, and the time required for post-processing is less than the printing speed, the control unit can reduce the forward rotation speed of the inversion unit when the printed print medium is fed into the inversion unit and recalculate the double-sided transport speed.

In addition, in the double-sided printing device of the present invention, if the double-sided transport speed calculated by lowering the normal rotation speed of the inversion unit is less than the printing speed, the control unit can recalculate the double-sided transport speed by changing the stop time of the print medium in the inversion unit within the range of the paper spacing according to the time required for post-processing.

In addition, in the double-sided printing device of the present invention, when the double-sided transport speed calculated based on the paper spacing corresponding to the size of the print medium, the printing speed, and the time required for post-processing is less than the printing speed, the control unit can change the stop time of the print medium in the inversion unit within the range of the paper spacing corresponding to the time required for post-processing and recalculate the double-sided transport speed.

1 Inkjet printing device 10, 110 Side paper feed section 11, 111 Paper feed tray 12, 112 Primary paper feed section 14, 114 Secondary paper feed section 14a, 114a Registration roller 15, 115 Vertical conveying roller 20, 120 Internal paper feed section 21a, 21b, 121a, 121b, 121c Paper feed tray 22a, 22b, 122a, 122b, 122c Primary paper feed section 23 Conveying roller 30, 130 Printing section 31, 131 Line head 32, 132 Conveying belt 40, 140 Paper discharge section 41, 141 Paper discharge tray 42, 142 Paper discharge roller 43, 143 Switching mechanism 50, 150 Reversing section 52, 152 Reversing roller 60, 160 Control section 70, 170 Operation panel HS Discharge transport paths P, P1, P2 Print medium RS Reverse transport sensor SR Reverse transport path DS1 First double-sided transport path DS2 Second double-sided transport path CR Circulation transport path FR Paper feed transport path

Claims (9)

a printing unit that performs printing processing on a print medium;
a registration unit that feeds the printing medium toward the printing unit at regular intervals;
a reversing unit that receives the printed medium, one side of which has been printed by the printing unit, and reverses and discharges the printed medium;
a control unit for controlling a transport speed of the print medium,
A double-sided printing device in which the control unit calculates, based on the size and printing speed of the printing medium, the number of sheets of printing medium in the printing medium transport path and the double-sided transport speed when circulating the printed printing medium and re-feeding it to the registration unit, and if the calculated double-sided transport speed is outside a predetermined range, the control unit changes the number of sheets of printing medium in the transport path and the control conditions of the inversion unit to recalculate the double-sided transport speed. The double-sided printing device according to claim 1, wherein the control unit changes the control conditions of the inversion unit and recalculates the double-sided transport speed when the double-sided transport speed calculated based on the size of the print medium and the printing speed is less than the printing speed. The double-sided printing device according to claim 2, wherein the control unit, when the double-sided transport speed calculated based on the size and printing speed of the print medium is less than the printing speed, reduces the normal rotation speed of the inversion unit when the printed print medium is fed into the inversion unit, and recalculates the double-sided transport speed. A duplex printing device according to claim 3, wherein the control unit changes the stop time of the print medium in the reversing unit and recalculates the duplex transport speed if the duplex transport speed calculated by lowering the normal rotation speed of the reversing unit is less than the printing speed. A double-sided printing device according to claim 2, wherein the control unit changes the stop time of the print medium in the inversion unit and recalculates the double-sided transport speed when the double-sided transport speed calculated based on the size of the print medium and the print speed is less than the print speed. The double-sided printing device according to claim 1, wherein the control unit calculates the number of sheets of print media in the print media transport path and the double-sided transport speed when circulating and transporting the printed print media to be re-fed to the registration unit based on the size of the print media, the printing speed, and a paper interval corresponding to the time required for post-processing in a post-processing device connected to the double-sided printing device. The double-sided printing device according to claim 6, wherein the control unit, when the double-sided transport speed calculated based on the size of the print medium, the printing speed, and the paper interval corresponding to the time required for post-processing, is less than the printing speed, reduces the normal rotation speed of the inversion unit when the printed print medium is fed into the inversion unit, and recalculates the double-sided transport speed. The double-sided printing device according to claim 7, wherein the control unit recalculates the double-sided transport speed by changing the stop time of the print medium in the reverse unit within a paper gap range according to the time required for the post-processing, when the double-sided transport speed calculated by lowering the normal rotation speed of the reverse unit is less than the printing speed. A duplex printing device according to claim 6, wherein, when the duplex transport speed calculated by the control unit based on the size of the print medium, the printing speed, and the paper spacing corresponding to the time required for post-processing is less than the printing speed, the control unit changes the stop time of the print medium in the inversion unit within the range of the paper spacing corresponding to the time required for post-processing, and recalculates the duplex transport speed.